Tire leak detector circuit

This is the circuit principle of the tire leakage detector . The airflow sound from the leaking part of the car inner tire after being punctured by a sharp object
is received by the microphone S and converted into an electrical
signal. It is coupled to the transistor VT through the capacitor C2
for amplification, and then passes through the coupling capacitors Ca and C4 and the volume is selected by the potentiometer
RP. The integrated power amplifier
SL31 fully amplifies the sound and is played back by headphones.
    The tire leakage detector uses a low-voltage integrated
power amplifier circuit SL31 (or LA4101). Its
operating voltage can be selected between 2~4, 5V, and the current
working power supply is 3V. The transistor VT uses silicon NPN
transistor 3DG8. Its own noise is small, which is
helpful to identify air leakage faults. The value should be above 120, and the penetration current Ieffi should be less than 1-L. Headphones can use 8n low-impedance earplugs. The electret microphone uses a non
-directional miniature electret capacitive sensor CR22-9B. The remaining resistors and capacitors are all small components. The outer shell can be made of a transistor small radio plastic
shell, with a size of about 68mm × 58mm. The working power supply uses two R-type batteries connected in series. Small synthetic membrane potentiometer WH15-K22
type for potentiometer W, with power switch